The invention concerns a monitoring device for delivering an alarm signal by means of an alarm transmitter in dependency on the counter result of a counter with at least one roller, particularly a kilometer counter, with a first sensing element which has a predetermined roller position for the emission of a first position-dependent signal.
Particularly in connection with electrically driven odometers in vehicles, the desire exists, after a given distance is covered, to produce an alarm signal which signalizes for example, certain maintenance or inspection operations. An electromotor driven counter provided for this comprises a roller or cylinder which, for example, completes a 90.degree.--rotation upon reaching each 10,000 counter units--kilometers--and catches or locks in this position. This means that, starting out from an initial position of 0.degree. with a roller position of 90.degree., 10,000 kilometers are indicated; with a roller position of 180.degree.--20,000 kilometers; with a roller position of 270.degree.--30,000 kilometers; with a roller position of 360.degree. or 0.degree.--40,000 kilometers and--with a second arrival of the roller into the 90.degree. position--50,000 kilometers.
If, with such a counter with a sensing element, a higher counter position is to be monitored, the problem exists that the roller reaches the roller position assigned to this higher counter value not only at this higher counter value but also before, at a lower counter value, with a previous rotation. In the preceding example, this means that the roller position for the counter value 50,000 kilometers already appears before with a first rotation of the roller with the attainment of 10,000 kilometers.
It is the object of the present invention to create such a monitoring device which for monitoring of higher counter values, by which counter values the roller of the counter has completed more than one rotation, no false alarm occurs with a lower counter value and with which the movement of the counter is impeded as little as possible by the monitoring device, in order for the counter to be able to be driven trouble-free by a motor with a low moment of rotation. Moreover, the sensing or scanning detection of the roller position should take place preferably without contact by means of the sensing element.